The invention relates to an apparatus and method for making a fiber reinforced plastic structural component having curved surface sections, and the product so produced. Fiberglass, Carbon and Kevlar fiber reinforced plastics can be molded into various structural shapes having excellent strength-to-weight ratios, and can be used for constructing a wide variety of structures. One popular present method of making structural parts from such materials is to pre-impregnate a fabric with an appropriate resin, partially cure the resin to a "B" stage, and bring layers of the pre-impregnated partially cured fabric together into a suitable mold wherein they are completely cured under heat and pressure. The ratio of resin to fiber is important in the final composite, and the density and uniformity of the cured part is affected by the entrapped air and/or other gases formed during the cure cycle. To alleviate the entrapped gas problem and to control the resin content of the final product, a specified amount of partially cured resin is "bled" away from the composite under vacuum while the gases are allowed to escape. One method of controlling the "bleeding" process is the use of a bleeder cloth, the bleeder cloth being placed on a release liner which is disposed on top of the pre-impregnated fabric to be cured. The release liner is open meshed and allows the gases and resin to permeate through the bleeder cloth, and the bleeder cloth then entraps the excess resin.
Presently, woven fiberglass fabric (181 for example) is used as a bleeder cloth. After heat cleaning, such a fabric has the required resin-holding capacity and air porosity to do the job, and is free of any contaminants that might interfere with the curing of the resin. For flat structures, fiberglass does an excellent job, however, for structures requiring curvatures (especially sharp curvatures) the inelastic properties of the woven fiberglass require that the fabric be cut and fitted around the curved areas of the mold. This is a laborious and exacting procedure which sometimes causes an inexact seating of the mold, with defective parts resulting (having excessive voids, inexact contours, etc.).
According to the present invention, a bleeder cloth is used for making structural components of fiber reinforced plastic which does not have the drawbacks mentioned above with respect to fiberglass fabric in the making of structural components having curved surface sections. The bleeder cloth according to the present invention comprises a textile-like non-woven fabric comprising polyester fibers locked into place by fiber interaction, the fabric having a regular repeating pattern of entangled fiber regions of higher area density than the average area density of the fabric and interconnecting fibers which extend between the dense entangled fiber regions and which are randomly entangled with each other in said regions, said fibers of the fabric being locked into place by a three-dimensional fiber entanglement characterized by a fiber-interlock value due to fiber entanglement of at least 7 with a fiber entanglement completeness of at least 0.5, said values being determined in the absence of binder, and wherein fibers in said regions turn, wind, twist back and forth, and pass about one another in all directions of said regions in such an intricate entanglement that fibers interlock with one another when the fabric is subjected to stress, to thereby provide coherency and strength to the fabric. Such a textile-like fabric, and the method of making same, is more fully disclosed in U.S. Pat. No. 3,485,706, the disclosure of which is hereby incorporated by reference in the subject application. By the term "bleeder cloth" is meant a cloth that has sufficient air porosity to allow the relatively free passage of air therethrough, good resin-holding capacity, and absence of any contaminants that might interfere with resin curing. It is distinguished from a "release coated fabric" or "release liner" which allows the passage of both air and resin therethrough, and which provides a surface that will not stick to the structural components being formed.
The bleeder cloth according to the present invention is easier to handle than the prior art fiberglass fabric, and can consistently produce curved-surface structural components of higher quality (less voids and more uniform surface areas) than the prior art. This is because the bleeder cloth according to the invention has excellent stretch and set properties for ready conformation around compound curves; there is no need to cut and fit the fabric, but rather the fabric is simply laid into a mold and it stretches and conforms when pressure is applied. Yet the bleeder cloth of the invention is capable of transmitting pressures that are imposed on it properly to the pre-impregnated fabric, which is essential in order for proper end product formation. The bleeder cloth according to the invention has the following properties which make it ideal as a bleeder cloth: sufficient air porosity to allow the escape of gases during curing and so that it does not become clogged prematurely as the resin cures; capacity to move the mobilized resin through its structure; sufficient resin holding capacity to prevent resin rich composite; clean and free of materials that may interfere with the curing of the resin; non-slip surface so that it will stay where placed; and elongation in both directions for conformability. Some of these properties are quantified as follows: Wt: about 1.9 oz/sq. yd.; elongation: 35-50% MD, 65-80% XD; Drape (Handlometer): 8 MD, 5 XD; Nonfibrous content: 0.5% (In the above MD means in the machine direction, and XD in the cross-machine direction).
An assembly for producing a fiber reinforced plastic structural component from a resin pre-impregnated partially cured fabric, comprises a first mold section having curved portions, and coated with a release layer, and adapted to receive at least one layer of the resin impregnated partially cured fabric on the interior thereof, a release coated fabric adapted to be disposed on the resin pre-impregnated fabric when the fabric is on the first mold section, at least one layer of bleeder cloth disposed on the release fabric, the bleeder cloth comprising a textile-like non-woven polyester fabric as described in U.S. Pat. No. 3,485,706, a second mold section, and means for evacuating gas from the area between the mold sections. The second mold section may comprise a male mold section comprising an expandable silcone rubber section, the male section transmitting pressure to the bleeder cloth and release fabric when pressure is applied thereto.
The method for producing a fiber reinforced plastic structural component having curved surface sections from a resin pre-impregnated, partially cured fabric, according to the present invention, comprises the steps of disposing at least one layer of the resin pre-impregnated fabric on a first mold section having curved portions, disposing a release coated fabric on the resin impregnated fabric, disposing at least one layer of the bleeder cloth according to the present invention on the release fabric to draw and hold excess resin from the resin impregnated fabric, disposing a second mold section over the at least one layer of bleeder cloth, applying pressure to all the components in the mold formed by the mold sections, and evacuating the gases through the release fabric and the at least one layer of bleeder cloth while heating all the components of the mold to completely cure the resin pre-impregnated fabric.
The fiber reinforced structural component with curved surface sections according to the present invention is a component produced by disposing at least one layer of resin pre-impregnated partially cured fabric on a first mold section, disposing a release coated fabric on the at least one layer of resin impregnated fabric, disposing at least one layer of bleeder cloth on the release fabric to draw and hold excess resin from the resin pre-impregnated fabric (the bleeder cloth being a polyester textile-like non-woven fabric as shown in U.S. Pat. No. 3,485,706), disposing a second mold section over the at least one layer of bleeder cloth, applying pressure to all the components in the mold formed by the mold sections, and evacuating gases through the release fabric and the at least one layer of bleeder cloth while heating all the components of the mold to completely cure the resin pre-impregnated fabric.
It is a primary object of the present invention to provide an improved assembly and method for producing an improved fiber reinforced structural component with curved surface sections. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.